Method and apparatus for damping/absorbing rotational vibrations/oscillations

ABSTRACT

A vibration damping device for use with a downhole tool having a tool axis may comprise a device housing mechanically coupled to the downhole tool, wherein the device housing defines a receptacle having a volume and an inner surface; an inertia element movably supported in the receptacle and having a volume, a mass, and a non-zero moment of inertia about the tool axis; wherein the inertia element volume is greater than the receptacle volume and an interstitial volume is defined between the inertia element and the receptacle, and wherein the interstitial volume is occupied by a fluid or an elastomer. The device may include a longitudinal bearing and/or a radial bearing between the inertia element and the receptacle. The device may also include a pressure compensation device in fluid communication with the receptacle and positioned within or an integral part of the device housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional application which claims priorityfrom U.S. provisional application No. 62/952,233, filed Dec. 21, 2019,which is incorporated by reference herein in its entirety.

TECHNICAL FIELD/FIELD OF THE DISCLOSURE

The present disclosure relates generally to damping vibrations orrotational oscillations during drilling operations using rotarysteerable systems, and specifically to inertial damping systemsconverting vibration energy into heat energy, resulting in the desireddamping effect.

BACKGROUND OF THE DISCLOSURE

In hydrocarbon drilling operations, boreholes are typically drilled byrotating a drill bit attached to the end of a drill string. The drillbit can be rotated by rotating the drill string at the surface and/or bya fluid-driven downhole mud motor, which may be part of a bottom holeassembly (BHA). For example, a mud motor may be used when directionaldrilling using a rotary steerable system (RSS). The combination offorces and moments applied by the drill string and/or mud motor andforces and moments resulting from the interaction of the drill bit withthe formation can have undesirable effects on the drilling system,including reducing the effectiveness of the cutting action, damage toBHA components, reduction in BHA components life, and interference inmeasuring various drilling parameters.

SUMMARY

To mitigate such negative effects, a BHA may be equipped with a dampingsystem to draw vibration energy from the BHA and thereby damping theeffects associated with torsional vibration excitation.

A vibration damping device for use with a downhole tool adapted torotate about a tool axis, may comprise a device housing. The devicehousing may be configured as a cartridge that is mechanically coupled toa downhole tool. The housing may comprise an annular wall having acentral bore therethrough. The device housing may define a receptaclehaving a volume and an inner surface and an inertia element may bemovably supported in the receptacle. The inertia element may have avolume, a mass, and a non-zero moment of inertia about the tool axis.The volume of the inertia element may be less than the volume of thereceptacle so that an interstitial volume may be defined between theinertia element and the receptacle. The interstitial volume may beoccupied by a fluid or an elastomer. The inertia element may besupported within the receptacle in a manner that allows the inertiaelement to move relative to the device housing.

The device may further include a pressure compensation device. Thepressure compensation device may comprise a pressure compensationhousing and a piston moveably mounted therein so as to define a variablecompensation volume. The variable compensation volume may be in fluidcommunication with the receptacle. The device may further include atleast one longitudinal bearing and at least one radial bearing, eachbearing positioned between the inertia element and the inner surface ofthe receptacle.

The pressure compensation housing may be formed separately from thedevice housing. If present, the pressure compensation housing may bereceived within the device housing. Alternatively, the pressurecompensation housing may comprise the device housing.

The device may further include, positioned between the inertia elementand the inner surface of the receptacle, at least one of a longitudinalbiasing means and longitudinal friction pad combination or a radialbiasing means and radial friction pad combination.

The device may include at least one of a longitudinal bearing and aradial bearing positioned between the inertia element and the innersurface of the receptacle and, positioned between the inertia elementand the inner surface of the receptacle, at least one of a longitudinalbiasing means and longitudinal friction pad combination or a radialbiasing means and radial friction pad combination.

The device housing and receptacle may be configured such that movementof the inertia element relative to the device housing can compriserotation through 360 degrees about the tool axis. The device housing maycomprise a collar configured to be part of a drill string. The devicehousing may be affixed to or integral with a drill bit.

The inertia element may have an outer radius less than the outer radiusof the housing, the inertia element may have an inner radiussubstantially equal to the radius of the central bore, and thereceptacle may be in fluid communication with the central bore.Alternatively, the inertia element may have an outer radiussubstantially equal to the outer radius of the housing, the inertiaelement may have an inner radius greater than the radius of the centralbore, and the receptacle may be in fluid communication with theenvironment surrounding the housing.

The inertia element may have a shape selected from the group consistingof square toroids, tori, and azimuthally-spaced segments.

A method for providing a damping tool for use with a bottomhole assembly(BHA), the damping tool including a torsional damping device and thetorsional damping device including an inertia element and a dampingfluid, may comprise the steps of:

-   -   a) calculating a set of natural frequencies and mode shapes of        the BHA based on the mechanical properties of the BHA;    -   b) selecting at least one desired frequency from the calculated        natural frequencies;    -   c) calculating or measuring the frequency dependent damping        response of a damping device and adjusting at least one property        of the damping device so that the calculated or measured        frequency dependent damping response corresponds to the at least        one desired frequency; and    -   d) using the calculated mode shapes to determine where to couple        the damping device to the BHA.

The method may further include the steps of calculating, for at least aselected natural frequency of the BHA, the amplitude of vibration foreach point along the BHA, identifying at least one location on the BHAat which amplitude of vibration at the selected natural frequency has azero value and positioning the damping tool at the identified location.The BHA may comprise a drill bit. Step c) may comprise adjusting one ormore properties selected from the group consisting of the mass of theinertia element, material density of the inertia element, moment ofinertia of the inertia element to the tool axis, shape of the inertiaelement, shape of the tool, density of the damping fluid, and viscosityof the damping fluid, and selecting a value that results in a dampingtool frequency that most closely matches the desired frequency. Thetorsional damping device may comprise a housing mechanically coupled tothe downhole tool, the housing comprising an annular wall having acentral bore therethrough. The wall may include a receptacle having avolume, and an inertia element may be movably supported in thereceptacle. The inertia element may have a volume, a mass, and anon-zero moment of inertia about the tool axis. The volume of thereceptacle may be greater than the volume of the inertia element so asto define an interstitial volume therebetween and the interstitialvolume may be occupied by a fluid or an elastomer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic view of a drilling system in which embodiments ofthe current invention can be used.

FIGS. 2-4 schematically illustrate possible locations for a dampingdevice and its different setups for installation in a drilling system.

FIGS. 5-7 schematically illustrate possible locations for a dampingdevice and its different setups for installation in a drilling system.

FIG. 8 is a cut-away view of a device in accordance with an embodimentof the invention.

FIGS. 9-10 illustrate alternative embodiments of the device of FIG. 8.

FIG. 11 is a cut-away view of a device in accordance with anotherembodiment of the invention.

FIG. 12 is a cross-section illustrating one component of the embodimentof FIG. 11.

FIGS. 13-14 are cross-sectional and isometric partial cutaway views,respectively, of another embodiment of the invention.

FIG. 15 is a schematic cross-section illustrating another embodiment ofthe invention.

FIG. 16 is a schematic cross-section illustrating another embodiment ofthe invention.

FIG. 17 is a schematic illustration of torsional vibrational nodes ofpart of a drill string.

FIGS. 18A and 18B are plots of models illustrating damping of torsionalvibration at target frequencies.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Referring initially to FIG. 1, a drilling system 100 in which thepresent apparatus may be used may include a drilling rig 101 positionedabove a wellbore 102 that extends into a subsurface formation 110. Adrill string 105 may extend from drilling rig 101 into wellbore 102 andmay terminate in a bottom hole assembly (BHA) 103. Drill string 105 maybe driven by the surface equipment of the rig. In some embodiments, BHA103 may include a drill bit 107, a motor 106, which may be a mud motoror other downhole motor, and a steerable system 104, which may be arotary steerable system (RSS). BHA 103 may optionally include variousother devices, such as logging or measurement devices, communicationsdevices, and the like. If present, steerable system 104 may be used tosteer the bit as the wellbore is drilled. The rotational force (torque)required to rotate drill bit 107 can be provided a torque creating orapplying apparatus, which may be a drill string 105, motor 106, or acombination thereof.

According to FIGS. 2-4, in some embodiments, one or more damping devices10 may be positioned between the torque applying or creating apparatusand drill bit 107. By way of example only, a damping device 10 may bepositioned between drill string 105 and drill bit 107 or betweensteerable system 104 and drill bit 107. Alternatively or additionally, adamping device may be part of the drill bit. In FIG. 2, damping device10 is integrated in BHA 103. In FIG. 3, damping device 10 is provided onone or more standalone subs as an add-on to BHA 103. FIG. 3 shows a“modular” device, in which the functional features can be selectivelyadded or removed at a rigsite. FIG. 4 shows a setup in which thefunctional features are integrated into a different component of the BHA(e.g. a stabilizer or a flex sub). If the damping device is included(integrated) in the BHA, adding or removing the damping device at therigsite is only possible if the entire BHA component is added orremoved. The optimal position of the damping device depends on amultitude of parameters. Optimal efficacy is reached when placed at ananti-node of the respective modal-shape.

The damping device may be part of any BHA component. FIGS. 5-7 showvarious possible locations for the damping device 10 in the drillstring.Specifically, FIG. 5 shows several possible locations for the dampingdevice 10 on a motor driven RSS BHA. FIG. 6 shows several possiblelocations for damping device 10 on a conventional motor driven BHA. FIG.7 shows several possible locations for damping device 10 on aconventional BHA without motor and RSS.

Referring now to FIG. 8, some embodiments of damping device 10 comprisea housing 52, a receptacle 54 defined within housing 52, and at leastone component with significant torsional inertia, illustrated as inertiaelement 50, disposed in receptacle 54. As used herein, “torsionalinertia” refers to the tendency of an element to resist a change ofrotation rate. In some cases, the torsional inertia of inertia element50 should be as great as possible. In order to be effective, inertiaelement 50 has certain minimum desired inertia. The minimum desiredinertia depends on the energy to be dissipated and can be adapted to thespecific application.

In some embodiments, housing 52 may include an annular housing wall 55defining a coaxial bore 56 and a coaxial cylindrical surface, which mayserve as a fluid passage. The thickness of housing wall 55 is a matterof design preference and depends in part on the magnitude of drillingloads (torque, bending, etc.) that are expected to be conducted througheither the housing or the receptacle. Inertia element 50 can be anyshape having a non-zero moment of inertia about the longitudinal(rotational) axis 53 of the drill string. By way of example, inertiaelement 50 may be a square toroid (as illustrated), a torus, a pluralityof azimuthally-spaced segments, or other distribution of mass withinhousing 52.

As discussed above, damping device 10 may be positioned on a componentof the BHA. In such embodiments, damping device 10 may be coupled to thecomponent by a common form-locked and/or force-locked connection, suchas a press fit between bore 56 and a through-going shaft or between thecylindrical surface and a coaxial bore in said component, a serration,or the like. More than one damping device 10 may be placed at onelocation on a component of the BHA and damping devices 10 may be placedat more than one location on a BHA. Each of the plurality of devices mayprovide different damping. The devices may be similar except for theirfluids and/or the inertia elements.

Referring briefly to FIGS. 9-10, housing 52 and the position of inertiaelement 50 therein may have any suitable configuration, including butnot limited to the embodiments shown at 52, 52′, and 52″, in whichinertia elements 50, 50′, and 50″ and receptacles 54, 54′, and 54″,respectively, have different configurations.

Receptacle 54 is configured such that the volume of receptacle 54 isgreater than the volume of inertia element 50 and defines aninterstitial volume therewith. As set out in detail below, theinterstitial volume, i.e., the volume of receptacle 54 that is notoccupied by inertia element 50, may be filled with one or more fluidsand/or elastomers.

Referring now to FIGS. 11 and 12, in an alternative embodiment, inertiaelement 50 may be housed in a cartridge 76. Damping device 10 or, ifconfigured as a cartridge, cartridge 76 may be mechanically coupled to acomponent of the BHA or otherwise mounted so as to transmit torsionalvibrations and/or accelerations from the drill string 105 to thecartridge 76 and thereby to the contents of the cartridge 76, such asinertia element 50 and a comprised fluid. If a cartridge 76 is present,the interior of the cartridge may define receptacle 54. In someembodiments, cartridge 76 may be configured to be easily removed orreplaced and/or to allow easy access to the contents of the cartridge.

In some embodiments, since the device is subject to well boreconditions, the fluid pressure in receptacle 54 may be adjusted to thepressure in the well bore using an optional pressure compensationfeature 57. If present, pressure compensation feature 57 may be part ofor attached to cartridge 76. FIG. 12 illustrates an exemplary embodimentin which a pressure compensation feature 57 comprises a compensationpiston housing 82 having compensation piston 84 moveably mountedtherein. Together, compensation piston housing 82 and compensationpiston 84 define a variable compensation volume 86. Compensation piston84 may or may not be equipped with a biasing means that tends to reducethe volume of compensation volume 86. Compensation volume 86 may be influid communication with receptacle 54 and thus filled with the samefluid as the interstitial volume. Movement of compensation piston 84inside compensation piston housing 82 adjusts compensation volume 86 toachieve a pressure equilibrium between fluid in the well bore and fluidinside damping device 10.

In some embodiments (not shown), instead of being provided inconjunction with cartridge 76, pressure compensation feature 57 may beincorporated into or formed as part of housing 52. In these embodiments,compensation piston housing 82 and device housing 52 may be a singleelement and fluid communication between the wellbore and the back sideof compensation piston 84 may comprise a fluid channel extending througha portion of housing 52, such as housing wall 55.

Relative movement between inertia element 50 and drill string 105 ispartially restricted by friction generated as inertia element 50 moveswithin receptacle 54. As a result, some of the kinetic energy of thedrill string is dissipated as heat. Because of the transformation ofkinetic energy into heat, the damping fluid may expand, increasingpressure inside receptacle 54. In some embodiments, housing 52 maycontain the pressure and in some embodiments pressure compensationfeature 57 may be used to maintain a desired fluid pressure inreceptacle 54. Alternatively or additionally, the gap(s) between theouter diameter of housing and adjacent equipment may be eliminated orfilled with a thermally conductive material so as to enhance theconductance of heat away from housing 52 and create a path for removingthe generated heat.

The embodiment of FIG. 12 also includes a two-part housing 52,comprising an outer housing 52 a and an inner housing 52 b. Housing 52may comprise a single element or may comprise an assembly of two or moreparts, which may be, by way of example only, welded together.

In some embodiments, inertia element 50 can be supported withinreceptacle 54 in a manner that allows inertia element 50 to rotate aboutaxis 53 without contacting the walls of receptacle 54. Still referringto FIG. 12, in some embodiments, the support for inertia element 50 mayoptionally include longitudinal bearings 60 and/or radial bearings 70 inaddition to a fluid. Longitudinal bearings 60 may be positioned betweenthe end(s) of inertial element 50 and the inner surface of receptacle54. Radial bearings 70 may be positioned between the inside and/oroutside of inertial element 50 and the inner surface of receptacle 54.Bearings 60, 70 can be sliding bearings or roller bearings. If present,longitudinal and/or radial bearings 60, 70 can be configured such thatinertia element 50 rotates around the centerline of the damping device10. In some embodiments, inertia element 50 is disposed in housing 52 ina manner that allows at least some rotation of inertia element 50 aboutaxis 53 relative to housing 52. In some embodiments, rotation of inertiaelement 50 about axis 53 is not restricted; in such embodiments, it ispossible for inertia element 50 to rotate through 360 degrees.

If present, longitudinal and/or radial bearings 60, 70 can also beconfigured such that a certain predetermined gap between housing andinertia ring is maintained. One function of bearings 60, 70 is tomaintain a substantially uniform circumferential gap by preventinginertia element 50 from coming into contact with the inner surface ofreceptacle 54. A second function is functional separation. In preferredembodiments the friction is generated primarily by the fluid, which isfree from wear, deterioration and undesired properties. In somealternative embodiments (e.g. FIGS. 15 & 16) bearings 60, 70 may besimilar to friction pads (discussed in detail below) and may serve bothpurposes (separation and friction) simultaneously.

Referring briefly to FIGS. 13-14, in other embodiments, inertia element50 may be provided as two or more individual inertia elements, such asthose illustrated at 50 a, 50 b, and 50 c. Individual inertia elements50 a, 50 b, and 50 c may be provided within a single cartridge 76, asshown in FIG. 13, or may be provided in separate cartridges 76 a, 76 b,76 c, as shown in FIG. 14. Inertia elements 50 a, 50 b, and 50 c maydiffer in their individual inertias by i) having a different volume, ii)being made of materials having different densities, iii) havingdifferent moments of inertia, or a combination of these options.

Regardless of the configuration of the inertia element 50 and receptacle54, in some embodiments the interstitial volume between inertia element50 and receptacle 54 may be filled with a fluid. In such instances, theportion of receptacle 54 that is not occupied by inertia element 50 maybe occupied by a specifically selected damping fluid, such as a viscousmedium including, for example, silicone oil. The damping fluid may havea high viscosity, such as for example up to 1,000,000 cSt at 25° C. Anexample of a suitable fluid is silicone oil. In some embodiments,housing 52 and/or pressure compensation feature 57 may each includeports and channels (not shown) for evacuating or filling pressurecompensation feature 57 and the volume between housing 52 and inertiaelement 50 with damping fluid.

In still other embodiments, the portion of receptacle 54 that is notoccupied by inertia element 50 may be occupied by an elastomer or one ormore elastomeric bodies. The elastomer needs to have specific elasticand damping properties so that it can deform and dissipate energy whiledeforming. For both choices (a high viscosity fluid and an elastomer) itis required that the molecular chains of the material move relative toeach other so as to dissipate energy. In addition, the elastomer ispreferably to be attached to both the housing 52 and the inertia element50 in order to transmit torque therebetween.

The presence of a viscous fluid or elastomer between the inertia element50 and the housing 52 will result in friction whenever inertia element50 moves relative to housing 52. The friction between inertia element 50and housing 52 allows the transmission of torque from housing 52 toinertia element 50. Because fluid is a poor transmitter of force and theelastomer is preferably selected to be likewise an absorber of force, aportion of the force imparted by housing 52 will be converted to heatinstead of being transmitted to inertia element 50. Thus, as vibrationsand/or rotational forces are transmitted to housing 52, they will beresisted and damped by the action of the inertial element on the fluid.

By way of example only and referring to FIG. 15, alternatively or inaddition to a damping fluid, damping device 10 may be equipped with oneor more pairs of longitudinal friction pads 62 that act in conjunctionwith one or more longitudinal biasing means 64 and inertia element 50.In the illustrated embodiment, longitudinal biasing means 64 urgesinertia element 50 toward one end of receptacle 54 and into engagementwith longitudinal friction pad(s) 62. Longitudinal biasing means 64 andpairs of longitudinal friction pad(s) 62 may each be provided at eitheror both ends of inertia element 50.

Alternatively or in addition to longitudinal compression and friction,and referring to FIG. 16, damping device 10 may be equipped with one ormore pairs of radial friction pads 72 that act in conjunction with oneor more radial biasing means 74 and inertial element 50. Radial frictionpads 72 may be radially inward and biasing means 74 may be radiallyoutward of inertia element 50, as shown, or vice versa. One radialfriction pad 72 may be affixed to biasing means 74 and a second radialfriction pad 72 may be affixed to inertia element 50, so that wheninertia element 50 rotates relative to housing 52, energy is dissipatedas heat at the interface between the two friction pads.

Each pair of friction pads 62, 72 defines a pad interface 63, 73,respectively, therebetween. By way of example, as illustrated at theleft-hand end of inertia element 50 (FIG. 15, as drawn), onelongitudinal friction pad 62 may be affixed to longitudinal biasingmeans 64 and a second longitudinal friction pad 62 may be affixed toinertia element 50, so that when inertia element 50 rotates relative tohousing 52, energy is dissipated as heat at the interface between thetwo friction pads. Friction pads 62, 72 may comprise any material orcombination of materials that provides a desired coefficient of frictionat pad interface 63 and can withstand the temperatures associated withthe downhole environment and the intended dissipation of energy.

In embodiments that include friction pads, the energy dissipationdepends, not on the medium in the interstitial volume, but on frictionbetween individual friction pads 62, 72. Thus, in this embodiment, it ispossible to replace the viscous damping fluid with any kind of fluid,even drilling mud. Thus, in certain embodiments, inertia element 50 doesnot need to be fully enclosed in housing 52 and receptacle 54, i.e. thevolume in which inertia element 50 is housed, may be in fluidcommunication with either the outside or the inside (bore) of thedrilling tool. By way of example, FIG. 9 illustrates an embodiment inwhich housing 52′ is configured such that receptacle 54′ is in fluidcommunication with bore 56 and FIG. 10 illustrates an embodiment inwhich housing 52″ is configured such that receptacle 54″ is in fluidcommunication with the environment outside of housing 52″. In eithercase, longitudinal bearings, longitudinal friction pads, andlongitudinal biasing means may optionally also be included in receptacle54, along with radial bearings, as described above.

Referring again to FIGS. 2-7, a damping device 10 can be used toincrease the reliability of an RSS and/or components of the RSS or BHA.Damping device 10 is especially advantageous in operations that have nodesignated vibration damping drill string component. Damping device 10can be integrated into a drill string as a separate device, and/or as aseparate device positioned within another drill string member(cartridge), or by integrating its components into a torque-transmittingmember of the drill string.

In some embodiments, damping device 10 can be tuned to at least onetorsional natural frequency of the tool or component it is intended toprotect, which may include, for example, the BHA, RSS, or othercomponents of the RSS. In these embodiments, the tool or component ismodeled and its natural frequency(ies) is(are) calculated.

According to some embodiments, damping device 10 can be adapted to adrill string or component thereof using the following steps:

-   -   a) Calculate the torsional natural frequencies, also referred to        as Eigen Values or eigenfrequencies, and mode shapes (Eigen        Vectors) based on the mechanical properties of the BHA (ODs,        IDs, Lengths, and Material Properties). The calculation may be        based on a finite elements analysis or the like. Boundary        conditions may be selected such that the system being examined        is free to rotate at one end and can be fixed, free, or weakly        supported at the opposite end.    -   b) Tune the damping device characteristics to match the desired        frequencies. Each damping device 10 will have frequency        dependent damping properties; tuning entails adjusting the        frequency dependent damping properties of the device to        correspond to the at least one desired frequency. The frequency        dependent damping properties can be adjusted by adjusting one or        more parameters including the inertia (mass, material density,        lever to axis of rotation, etc.) and damping characteristics        (type of fluid, fluid viscosity, shear gap width, shear gap        length, coefficient of friction, preload, etc.) of the damping        device. In some instances, the target frequency may be from 30        Hz up to 1000 Hz. The tuning may be carried out empirically or        using mathematical models.    -   c) Use the calculated mode shapes to select a location for the        damping device. As illustrated schematically in FIG. 17, for a        given tool and frequency, a mathematical model can be used to        calculate the amplitude of vibration at each point along the        tool. As illustrated in FIG. 17, the amplitude will tend to vary        between antinodes A1, A2, A3 . . . , i.e. points along the Eigen        Vector in which the amplitude is a local maximum or minimum,        along the length of the tool, with a node N (zero value) between        each pair of adjacent antinodes. Depending on the tool, the        antinodes may increase or diminish in amplitude along the length        of the tool, with the greatest amplitude (greatest maximum)        being closest to one end of the tool.

In some embodiments, it may be advantageous to position a damping device10 at each of one or more anti-nodes. In some instances, it may bedesirable to position a damping device 10 close to or at the point withthe largest absolute value of modal displacement. FIG. 18 illustratesdamping of torsional vibration measured in degrees (FIG. 18A) and rpm(FIG. 18B).

A system including one or more damping devices may be configured to dampvibrations at one or more frequencies. In some embodiments, dampingdevices tuned to different frequencies can be used to damp multiple(separate) frequencies. In other embodiments, a single damping devicethat is capable of damping a broad range of frequencies can be used. Theeffective frequency range of a damping device can be influenced byvarious parameters, as set out above.

The purpose of the present damping device is to protect the BHA, orcertain parts of said BHA, from torsional vibrations that exceeddetrimental magnitudes. In some instances, the device may be used fordamping loads that occur during drilling operation, such as torque peaksand/or torsional accelerations/oscillations. A drilling system mayinclude one or a plurality of said damping devices in differentlocations. The damping device can be an integral part of the BHA or oneof its components, where all needed elements are integrated into readilyavailable tools. It can also be added to the BHA as a separate device(module), where all elements are integrated into a tool on its own.

The foregoing outlines features of several embodiments so that a personof ordinary skill in the art may better understand the aspects of thepresent disclosure. Such features may be replaced by any one of numerousequivalent alternatives, only some of which are disclosed herein. One ofordinary skill in the art may readily use the present disclosure as abasis for designing or modifying other processes and structures forcarrying out the same purposes and/or achieving the same advantages ofthe embodiments introduced herein. One of ordinary skill in the art maymake various changes, substitutions, and alterations without departingfrom the scope of the present disclosure.

1. A vibration damping device for use with a downhole tool, the downholetool having a tool axis, the vibration damping device comprising: adevice housing mechanically coupled to the downhole tool, wherein thedevice housing includes a receptacle having a volume and an innersurface; an inertia element movably supported in the receptacle andhaving a volume, a mass, and a non-zero moment of inertia about the toolaxis; and a pressure compensation device, wherein the pressurecompensation device comprises a pressure compensation housing and apiston moveably mounted therein so as to define a variable compensationvolume, and wherein the variable compensation volume is in fluidcommunication with the receptacle; wherein the volume of the inertiaelement is less than the volume of the receptacle so that aninterstitial volume is defined between the inertia element and thereceptacle, and wherein the interstitial volume is occupied by a fluidor an elastomer; and wherein the inertia element is supported within thereceptacle in a manner that allows the inertia element to move relativeto the device housing.
 2. (canceled)
 3. The device of claim 1, andfurther including: at least one longitudinal bearing and at least oneradial bearing, each bearing positioned between the inertia element andthe inner surface of the receptacle; and a cartridge mechanicallycoupled to the downhole tool, wherein cartridge defines the receptacle.4. The device of claim 3, further including positioned between theinertia element and the inner surface of the receptacle, at least oneof: a longitudinal biasing means and longitudinal friction padcombination; and a radial biasing means and radial friction padcombination.
 5. The device of claim 3 wherein the pressure compensationhousing is formed separately from the device housing and the pressurecompensation housing and the cartridge are both received within thedevice housing.
 6. The device of claim 2 wherein the pressurecompensation housing comprises the device housing.
 7. The device ofclaim 2 wherein the pressure compensation housing is formed separatelyfrom the device housing and is received within the device housing. 8.The device of claim 1, further including at least one of a longitudinalbearing and a radial bearing positioned between the inertia element andthe inner surface of the receptacle.
 9. A vibration damping device foruse with a downhole tool, the downhole tool having a tool axis, thevibration damping device comprising: a device housing mechanicallycoupled to the downhole tool, wherein the device housing includes areceptacle having a volume and an inner surface; and an inertia elementmovably supported in the receptacle and having a volume, a mass, and anon-zero moment of inertia about the tool axis; wherein the volume ofthe inertia element is less than the volume of the receptacle so that aninterstitial volume is defined between the inertia element and thereceptacle, and wherein the interstitial volume is occupied by a fluidor an elastomer; and wherein the inertia element is supported within thereceptacle in a manner that allows the inertia element to move relativeto the device housing, further including positioned between the inertiaelement and the inner surface of the receptacle, at least one of alongitudinal biasing means and longitudinal friction pad combination ora radial biasing means and radial friction pad combination.
 10. Thedevice of claim 1 wherein the device housing and receptacle areconfigured such that movement of the inertia element relative to thedevice housing can comprise rotation through 360 degrees about the toolaxis.
 11. The device of claim 1 wherein the device housing comprises acollar configured to be part of a drill string.
 12. The device of claim1 wherein the device housing is affixed to or integral with a drill bit.13. The device of claim 1 wherein the housing comprises an annular wallhaving a central bore therethrough, wherein the inertia element has anouter radius less than the outer radius of the housing, wherein theinertia element has an inner radius substantially equal to the radius ofthe central bore, and wherein the receptacle is in fluid communicationwith the central bore.
 14. The device of claim 1 wherein the housingcomprises an annular wall having a central bore and an outer radius,wherein the inertia element has an outer radius substantially equal tothe outer radius of the housing, wherein the inertia element has aninner radius greater than the radius of the central bore, and whereinthe receptacle is in fluid communication with the environmentsurrounding the housing.
 15. The device of claim 1 wherein the inertiaelement has a shape selected from the group consisting of squaretoroids, tori, and azimuthally-spaced segments.
 16. A method forproviding a damping tool for use with a bottomhole assembly (BHA), thedamping tool including a torsional damping device and the torsionaldamping device including an inertia element and a damping fluid,comprising the steps of: a) calculating a set of natural frequencies andmode shapes of the BHA based on the mechanical properties of the BHA; b)selecting at least one desired frequency from the calculated naturalfrequencies; c) calculating or measuring the frequency dependent dampingresponse of a damping device and adjusting at least one property of thedamping device so that the calculated or measured frequency dependentdamping response corresponds to the at least one desired frequency; d)using the calculated mode shapes to determine where to couple thedamping device to the BHA.
 17. The method of claim 16, further includingthe steps of calculating, for at least a selected natural frequency ofthe BHA, the amplitude of vibration for each point along the BHA,identifying at least one location on the BHA at which amplitude ofvibration at the selected natural frequency has a zero value andpositioning the damping tool at the identified location.
 18. The methodaccording to claim 17 wherein the BHA comprises a drill bit.
 19. Themethod of claim 16 wherein step c) comprises adjusting one or moreproperties selected from the group consisting of the mass of the inertiaelement, material density of the inertia element, moment of inertia ofthe inertia element to the tool axis, shape of the inertia element,shape of the tool, density of the damping fluid, and viscosity of thedamping fluid, and selecting a value that results in a damping toolfrequency that most closely matches the desired frequency.
 20. Themethod of claim 16 wherein the torsional damping device comprises: ahousing mechanically coupled to the downhole tool, the housingcomprising an annular wall having a central bore therethrough, whereinthe wall includes a receptacle having a volume; an inertia elementmovably supported in the receptacle and having a volume, a mass, and anon-zero moment of inertia about the tool axis; wherein the volume ofthe receptacle is greater than the volume of the inertia element so asto define an interstitial volume therebetween and wherein theinterstitial volume is occupied by a fluid or an elastomer.